Although there are several types of systems for powering air guns, most air guns are powered by a power spring, e.g., a coil spring. The power spring actuates a hollow piston that covers or “skirts” the power spring. The piston includes a sear that engages a latch that is connected to a trigger assembly of the air gun.
Generally, in air guns that incorporate a contained power spring energy source, cocking the power spring, i.e., compressing the power spring creates a quantity of stored energy that can be released when desired by means of the trigger assembly to fire the air gun. When fired, the compressed power spring expands, moving the piston forward with in a compression tube to compress a quantity of air, which then launches a projectile.
These spring-powered air guns suffer from inaccuracy due to the hysteresis, vibration, and other harmonics resulting from the rapid unloading, decompression, or uncoiling of the power spring when fired.
There exist air-gunsmiths or “tuners” that offer special air gun charging system improvements claiming better performance to users that want more power and/or accuracy from their air guns. One of the primary benefits of tuning air guns is to reduce vibration when the power spring is released and the air gun is fired.
Some charging system improvements simply replace the entire original charging system with custom-fit components to reduce vibration. Others include modifying the charging system by adding nylon buttons to the outside surface of the piston tube itself to eliminate vibrations. While these prior art techniques for increasing air gun performance may achieve effective results for their intended purpose, they require significant modification to the air gun components and/or the replacement of most, if not the entire, charging system.
Referring now to Prior Art FIGS. 1 and 2, the general operation of a power spring charging system 1 of an air gun is described. The charging system 1 is illustrated in a cocked or ready-to-fire position in FIG. 1. Once a trigger 2 is pulled, a skirted piston 3 in the air gun compresses the air within an area 4 in a chamber of a compression tube 5 with a given force provided by a helical power spring 6 behind the head 7 of the piston 3. A dynamic seal or gasket 8 creates an air-tight seal between the piston 3 and an inner surface of the compression tube 5. A small washer-like guide member 9 has a rearward end that fits partially within the coils of the power spring 6 and a forward shoulder fits within the piston 3.
A rear guide tube 12 guides the power spring 6 at the rearward end of the charging system 1, and allows a sear rod 10 of the piston 3 to selectively engage a trigger assembly. A rearward shoulder 13 of the rear guide tube 12 provides a surface for the power spring 6 to press against, while an internal through bore 14 of the rear guide tube 12 allows the sear rod 10 to pass therethrough. All of these components, except the trigger assembly 11 are usually placed within a receiver tube 15 of the air gun.
The piston 3 is referred to as “skirted” as it includes a cylindrical tube or skirt 16 that extends back from the head 7 of the piston 3. The skirt 16 is concentric with the sear rod 10. The piston 3 is disposed within the cylindrical compression tube 5, and defines a compression chamber 4 between the head 7 and the compression tube 5. Compression tube 5 is disposed within the receiver tube 15 at the forward end of the receiver tube 15.
One inherent aspect of current air guns using coil spring charging systems is that when the power spring 6 is loaded, i.e., compressed, during cocking, the power spring 6 expands radially (i.e., its diameter increases). When the air gun is fired the power spring 6 fires forward and contracts radially back to it unloaded size. One disadvantage of current air guns is that this radial expansion and contraction of the power spring 6 during use necessitates that there is clearance between the inner wall of the skirt 16 of the piston 3 and the unloaded power spring 6. This clearance, however, allows forward movement and uncoiling of the power spring 6 during firing, which produces vibration both during and immediately after firing has occurred and the piston has come to a rapid stop. These vibrations are due, in part, to the power spring 6, which exhibits the characteristics of unwinding, torqueing and kinetic energy as it is released from its compressed state upon firing. This vibration or oscillation of the power spring 6, both during and immediately after firing, both reduce the power supplied by the power spring 6 and reduce accuracy of the air gun. Generally, the longer the power spring 6, the greater the amplitude of the vibrating deflection of the power spring 6. This deflection is greatest at the longitudinal midpoint of the power spring 6.